Method of Cooking a Food Item

ABSTRACT

A cooking apparatus has a user interface for selecting a cooking preference, a measurement sensor for measuring a distance between a pair of plates when a food item lies between the pair of plates, a weight sensor for measuring weight of the food item, and a control system for receiving at least one signal from the measurement and weight sensors to determine a cooking profile for cooking the food item to the cooking preference and to calculate a total amount of energy required to cook the food item according to the cooking profile and an amount of energy to be transferred per unit time to the food item, and to control power supply to the heating element based on the calculated amount of energy transferred per unit time to the food item.

This application is a Divisional Application of co-pending U.S.application Ser. No. 15/314,349 filed on Nov. 28, 2016, which is a U.S.nationalization under 35 U.S.C. § 371 of International Application No.PCT/AU2015/000325, filed May 29, 2015, which claims priority toAustralian Application No. 2014902073, filed May 30, 2014; the entirecontents of each are incorporated herein by reference.

The present invention relates to an apparatus for cooking food, and inparticular for cooking food between a pair of plates.

BACKGROUND

Food presses, such as sandwich presses or hamburger presses, use a pairof plates, whereby the sandwich, for example, is placed between a pairof heated plates to warm the bread and its filling. However, sandwichpresses rely on a user to insert the sandwich and monitor the time spentwarming the sandwich before removing it. As often happens, the user canbecome distracted and forget to remove the cooked sandwich, which thenburns. It is known to provide timing devices on sandwich presses toalert the user that the food item is cooked but these are not alwaysaccurate to properly cook the food item, and require setting by theuser.

On the other hand, food presses can also inconsistently cook food items,leading to undercooking. Taking for example sandwiches, thick sandwichesin particular are prone to undercooking, where the heat from the platesto the center of the sandwich takes a longer time to transfer thananticipated. To address this problem, the sandwich has to be squashedbetween the plates to improve heat transfer from the plates to thesandwich. This is undesirable as it inevitably crushes the sandwich,spilling its filling, and can generally affect the palatability of thesandwich.

Furthermore, inconsistent cooking may also cause food poisoningparticularly if the sandwich is not freshly prepared and insufficientheat has been applied to kill any bacteria.

It is desirable to provide a cooking apparatus that can accurately andconsistently heat or cook a variety of food items.

SUMMARY

In accordance with the invention, there is provided a cooking apparatuscomprising a pair of plates in between which a food item is to becooked, at least one of the plates having a heating element for cookingthe food item, the cooking apparatus having a user interface forselecting a cooking preference, a measurement sensor for measuring adistance between the pair of plates when the food item lies between thepair of plates, a weight sensor for measuring weight of the food item,and a control system for receiving at least one signal from themeasurement and weight sensors to determine a cooking profile forcooking the food item to the cooking preference and to calculate a totalamount of energy required to cook the food item according to the cookingprofile and an amount of energy to be transferred per unit time to thefood item, and to control power supply to the heating element based onthe calculated amount of energy transferred per unit time to the fooditem.

The cooking apparatus calculates and applies an amount and rate ofenergy input to cook the food item according to the cooking profile,which is a temperature cooking profile, based on the thickness and/orweight of the food item. The cooking profile specifies how the totalamount of energy required to cook the food item is transferred to thefood item during cooking.

Suitably, whilst cooking, the control system monitors and continuouslyadjusts the temperature to achieve the desired cooking outcome.

The cooking preference may be based on one or more variables includingtype of food item and the user's preferred cooking outcome for the fooditem. For example, a user can use the user interface to identify thetype of food item, for example, a piece of steak or chicken, and thedesired cooking outcome, for example, rare or well done.

The type of food item for which the control system may be programmed toinclude in a cooking preference includes, but is not limited to, fish,red meat, poultry, pork, vegetables and bread, or combinations thereofsuch as a sandwich. The preferred cooking outcome includes but is notlimited to ‘well done’, ‘medium’, ‘rare’ and ‘warm’, or a standardselection for food items including sandwiches such as ‘done’.

Based on the cooking preference, the cooking profile used to cook thefood item is determined by the control system. The cooking profile inturn determines the cooking temperature or range of cooking temperaturesto cook the food item to the cooking preference.

Suitably, the control system compares the amount of energy transferredto the food item to the total amount of energy required to cook the fooditem during the cooking process.

The comparison between the rate of energy transferred to the food itemand the total amount of required energy to cook the food item may becarried out continuously or at discrete intervals. For example, thecomparison may be conducted at 2, 5, 10, 15, 20 or 30 second intervals,or any time in between. Alternatively, the comparison may be conducted aset number of times before the projected completion time, for example,once or twice in the cooking process. Still alternatively, thecomparison may be continuous throughout the cooking process.

Preferably, the rate of energy transferred to the food item iscalculated per second of time.

In an embodiment, the control system predicts when the food item iscooked by monitoring the amount of energy transferred to the food item.The food item is predicted as cooked when the amount of energytransferred to the food item substantially equals the total amount ofenergy required to cook the food item.

In an embodiment, the cooking apparatus stops transferring energy intothe food item once the energy transferred to the food item issubstantially equal to the total amount of energy required to cook thefood item. In this respect, the control system stops supplying power tothe heating element once the energy transferred to the food item equalsthe amount of energy required to cook the food item.

In an embodiment, the control system reduces the power supply to theheating element to maintain the plates at a predetermined temperatureafter cooking completes.

Generally, the controller uses a closed loop transfer function (alsoknown as a feed forward system) to regulate the cooking temperature toensure that the food item is cooked according to the selected cookingpreference. In this respect, the controller identifies a specificcooking outcome for a selected food item and regulates the cookingtemperature to achieve the outcome.

In contrast, most conventional cooking apparatuses use a feedback systemwhereby temperature is set and the apparatus simply attempts to maintainthat desired setting, for example, a sandwich press. The user thendecides when the food item is cooked to their satisfaction. There is noclosed loop system generating a specified cooking outcome for a selectedfood item.

The control system preferably calculates the total energy required tocook the food item according to the cooking profile based on the weightof the food item. More preferably, the control system calculates theenergy required to cook the food item according to the cooking profilebased on the weight of the food item and temperature difference betweenthe selected cooking temperature to achieve the preferred cookingoutcome and the initial food item temperature.

The control system preferably calculates the total energy required tocook the food item according to the cooking profile based on the weightof the food item, the specific heat capacity of the food item, therequired cooking temperature to achieve the preferred cooking outcomeand the initial food item temperature.

The total energy required to cook the food item according to the cookingprofile may be calculated using the following equation, wherein Q is thetotal energy required to cook the food item according to the cookingprofile, C_(p) is the specific heat capacity of the food item, M is theweight of the food item, T₂ is the required (target) temperature toachieve the selected cooking preference and T₁ is the initial food itemtemperature:

Q=Mc _(p)(T ₂ −T ₁)

T₂ is preferably measured in the core of the food item.

The cooking temperature is the temperature required to achieve thetarget temperature of the food item. The cooking temperature may not bethe same as the target temperature. For example, the cooking temperaturemay be initially set higher than the target temperature in order to searthe food item, the cooking temperature may subsequently be lowered toensure that the food item does not overcook after searing.

The control system preferably calculates the amount of energytransferred to the food item per unit time during the cooking processbased on the thickness and/or weight of the food item. The controlsystem can also calculate the amount of energy transferred into the fooditem during the cooking process based on the change in temperature ofeach of the plates. For example, the amount of energy may be calculatedbased on the surface area of the food item in contact with the pair ofplates and the change in temperature of each of the plates of thecooking apparatus.

The energy (q) transferred to the food item per unit time may becalculated using the following equation:

q=ΔT ₁ R _(th) +ΔT ₂ R _(th), where ΔT_(1/2) =T _(plate1/2) −T_(food item temp)

ΔT₁ is the temperature difference between a first plate (T_(plate 1))and the food item temperature (T_(food item temp)) per unit time and ΔT₂is the temperature difference between a second plate (T_(plate 2)) andthe food item temperature (T_(food item temp)) per unit time.

Suitably, the first plate is a top plate of the cooking apparatus andthe second plate is a bottom plate of the cooking apparatus.

In an embodiment, the thermal resistance of the food item may becalculated based on the surface area of the food item in contact withthe pair of plates, the thickness of the food item and the thermalconductivity of the food item.

The thermal resistance (Rh) of the food item may be calculated using thefollowing equation, wherein A is the calculated surface area, (x) is themeasured thickness and (k) is the thermal conductivity of the food item:

$R_{th} = \frac{kA}{x}$

In an embodiment, the surface area (A) of the food item in contact withthe plates is calculated based on the thickness, weight and density ofthe food item.

The surface area (A) of the food item in contact with the plates may becalculated using the following equation, wherein (x) is the measuredthickness, (M) is the weight and (ρ) is the density of the food item:

$A = \frac{M}{x\rho}$

In another embodiment, the surface area of the food item in contact withthe plates is estimated using sensors. Preferably, the sensors aretemperature sensors. Other sensors such as pressure sensors may be used.

A temperature gradient exists between the surface and the core of thefood item. The surface temperature of the food item will be close to thesurface temperature of the plate in contact with the food item and thetemperature of the rest of the food item will be a function of thedistance from the plate, the heat capacity of the food item and thetemperature differential between the plate and the food item.

The calculated net food item temperature is cumulative, adding theincremental temperature gain to the previous temperature value.

On this basis, the amount of energy transferred into the food itemduring the cooking process may be calculated and measured against thetotal amount of energy required to cook the food item accordingly to thecooking profile. The cooking process completes when the amount of energytransferred to the food item equals the total amount of energy requiredto cook the food item.

The cooking profile may maintain the food item at a predeterminedtemperature after cooking. This may prevent the cooked food item fromgetting cold before it is consumed. This may avoid the need for aresting period after the food is cooked to allow the cooked food item toreach its target temperature.

Suitably, the predetermined temperature is the target temperature. Thismay allow the cooked food item to be maintained at the targettemperature for a prolonged period of time without overcooking. In thisembodiment, the plates are preferably made from a high thermalconductivity material to allow the temperature of the plates to reachthe predetermined temperature quickly from the cooking temperature. Incontrast, a low thermal conductive material increases the risk of thefood item overcooking due to an excessive amount of energy beingtransferred to the food item when the plates cool to the selectedtemperature.

Suitably, the thermal conductivity of the plates ranges from 30-400Wm⁻¹K⁻¹. Preferably, the thermal conductivity of the plates ranges from200-400 Wm⁻¹K⁻¹. More preferably, the thermal conductivity of the platesranges from 200-300 Wm⁻¹K⁻¹.

The cooking temperature and/or the cooking duration may be adjusted whenthe option to maintain the cooked food item at a predeterminedtemperature is selected.

The plates are relatively movable with respect to each other to lieagainst the food item therebetween. The plates are preferably paralleland may be oriented at any angle from a horizontal to a verticalposition. Suitably, the pair of plates are horizontally arranged todefine top and bottom plates in between which a food item is to becooked. Both plates suitably include heating elements, although theapparatus may function with only one element in one plate. Each platemay include two elements to provide temperature zoning. This allowsseparate food items to be cooked using different cooking profiles at atime.

In an embodiment, either or both plates may be made of aluminum.Suitably, either or both the plates further include a matrix of embeddedcopper and an outer coating of stainless steel.

In an embodiment, either or both plates may have high thermal inertia tomaintain sufficient heat to cook the food item.

Each plate may include a thermocouple for measuring the localtemperature and feedback to the control system. The initial temperatureof the food item may be measured by the thermocouple. The thermocouplemay also allow the cooking apparatus to determine the location of thefood item by measuring the temperature drop when a food item is placedon the plate. The temperature drop detected by the thermocouple may beused to estimate the surface area of the food item.

Suitably, each plate includes four thermocouples to improve the accuracyof the temperature measurement.

The pair of plates may be automated to be movable relative to oneanother and to maintain contact with the food item during the cookingprocess based on feedback from a plate pressure sensor.

One or both plates may include a plate pressure sensor to measurepressure of a plate against a food item during cooking and to transmit acorresponding signal to the control system to maintain a predeterminedpressure of the plate on the food item during cooking.

One of the plates may be automated to disconnect from the food itemafter completion of the cooking time.

The power output of each heating element may range from 50-5,000 W.Suitably, the power output of each heating element ranges from1000-1,200 W.

The user interface may include an LED screen for displaying the optionsavailable for selecting a cooking profile.

The measurement sensor (also known as a plate separation sensor) maytake many forms for measuring the distance between, i.e. the separationof, the plates.

The measurement sensor may be a position/angle/displacement sensorlocated at a pivot through which the plates are linked and rotated toseparate. The pivot may be a pivot of a lever arrangement wherespecifically the handle is levered to the cooking apparatus to open andclose one plate relative to the other. In this embodiment, themeasurement sensor measures the angle at which the handle is pivotedwhen a food item is placed between the pair of plates. The anglemeasurement is processed by the control system to calculate the distancebetween the pair of plates.

The measurement sensor may be located at any position on one or bothplates to measure the distance between the pair of plates. For example,the measurement sensor may be located on an edge of a plate andtransmits a signal to the other plate or another sensor on the otherplate to determine the positions of the pair of plates relative to eachother. Suitably, at least two measurement sensors are mounted on thefront and rear of the cooking apparatus.

The measurement sensor may be an acoustic or an optical sensor. Forexample, an ultrasonic sensor could be used for measuring distancebetween the pair of plates. The ultrasonic sensor transmits a signalfrom one plate that is reflected off the other plate and the time takenfor the signal to reflect back is used to measure the distance betweenthe plates.

The measurement sensor may be an optical/light sensor that uses a lightbeam to measure the distance between the pair of plates. For example,the sensor could be an infra-red sensor or an optical position sensor.Preferably, the sensor includes a plurality of light beams that can besequentially disrupted or blocked to measure the distance between thepair of plates.

The measurement sensor may have an accuracy ranging from 1-55 mm.Suitably, the accuracy ranges from 1-3 mm.

The measurement sensor may be located on one plate and comprises asliding pin mounted on one end to a printed circuit board located withinthe plate and on the other end to a guide mounted to a handle of thecooking apparatus. The sliding pin may be located on a side of the plateand is mechanically connected to the handle via a slot on the guide tobe movable with the relative separation of the plates. Movement of thehandle, which in turn moves the sliding pin, transmits a signal from themeasurement sensor to the control system which calculates the distancebetween the pair of plates.

The measurement sensor may measure the distance between the pair ofplates directly or indirectly. For example, an indirect measurementmethod involves measuring the angle at which a levered handle of thecooking apparatus is pivoted when a food item lies between the pair ofplates, and the distance between the plates is calculated using themeasured angle. An example of a direct measurement method involves usingan ultrasonic sensor to measure the distance between the pair of platesby transmitting a signal from one plate to the other.

The weight sensor may be in the form of a load cell. Suitably, the loadcell is positioned within or underneath the plate.

The weight sensor may have an accuracy ranging from 0.05-15%.

The user interface may be a control panel on the cooking apparatus, asmart phone app, a remote control or the like. The user interface mayinclude an LCD or LED display.

The control system may be a micro-processor PCB. The PCB may be mountedon a heat sink. A USB interface may be used for programming updates anda RJ45 network connection may be used for communicating with the userinterface. In an embodiment, the USB is used for logging data and amulti-pin connection ribbon is used to interface with a CPU forprogramming updates.

The control system may be programmed with predetermined settings ofspecific heat capacity, thermal resistance and thermal conductivityvalues, and alternatively or additionally, based on data received fromthe user interface.

The control panel includes an override for manually controlling thecooking profile regardless of the distance between the pair of plates orthe weight of the food item. For example, the cooking temperature may bemanually entered using the user interface into the control panel.

The override may also allow a user to cook a food item regardless ofwhether both plates are in contact with the food item. For example, whenthe top plate is lifted from the food item during cooking, the controlsystem allows the cooking process to continue on the basis that energyis only transferred via the lower plate. When the top plate re-contactsthe food item, the control system re-adjusts to continue the cookingprocess on the basis that energy is transferred via both plates. Thecooking apparatus may include a rack that is actuated to lift the fooditem off a bottom plate after completion of the cooking time. Actuationof the plates and/or the rack after completion of the cooking time isautomated by the control system.

The control system may switch off the heating element after completionof the cooking process. Alternatively or additionally, the controlsystem may transmit an audio and/or visual indication to alert a user ofcompletion of the cooking process.

The cooking apparatus may include zoned cooking areas, whereby each zonecomprises a heating element that is localized to function independentlyto heat the corresponding zone at an independent cooking profile to theother zones.

In accordance with the invention, there is also provided a controlsystem for a cooking apparatus, the cooking apparatus comprising a pairof plates, at least one of the plates having a heating element forcooking a food item, a measurement sensor for measuring a distancebetween the pair of plates when the food item lies between the pair ofplates, and a weight sensor for measuring a weight of the food item,wherein the control system is configured to:

-   -   receive data from a user interface to select a cooking        preference;    -   receive a signal from the measuring sensor to calculate the        distance between the pair of plates;    -   receive a signal from the weight sensor to determine the weight        of the food item;    -   determine a cooking profile to cook the food item according to        the cooking preference, where the cooking profile is determined        based on at least one signal from the measuring sensor and the        weight sensor;    -   calculate a total amount of energy required to cook the food        item according to the cooking profile based on the signal from        the weight sensor;    -   calculate an amount of energy per unit time to be transferred to        the food item per unit time based on the signal from the        measuring sensor;    -   switch on the heating element; and    -   control the heating element based on the cooking profile.

The control system may control the heating element to vary the amount ofenergy transferred to the food item per unit time. This, in turn, may beused to control the cooking time.

The control system may compare the amount of energy required to cook thefood item according to the cooking profile and the amount of energytransferred to the food item per unit time to determine the percentagecompletion of the cooking process.

The control system may compare the amount of energy transferred to thefood item to the total amount of energy required to cook the food itemat discrete intervals.

The control system may perform the following steps for controlling theheating element:

-   -   determine a time that has lapsed since the heating element is        switched on;    -   determine a temperature of the heating element based on the        cooking profile from the time since the heating element is        switched on;    -   measure a temperature of the heating element; and    -   control the heating element to either increase or decrease in        temperature based on the cooking profile and the current        temperature of the heating element to thereby either increase or        decrease the temperature of the heating element.

The control system may determine a cooking temperature based on thecooking profile.

The control system may calculate the total amount of energy required tocook the food item according to the cooking profile based on the weightof the food item.

The control system may predict when the food item is cooked bymonitoring the amount of energy transferred to the food item. The fooditem is predicted as cooked when the amount of energy transferred to thefood item substantially equals the total amount of energy required tocook the food item.

The control system may compare the amount of energy transferred to thefood item to the total amount of energy required to cook the food itemduring the cooking process.

The control system may stop the power supply to the heating element oncethe energy transferred to the food item is equals the amount of energyrequired to cook the food item.

The control system may reduce the power supply to the heating element tomaintain the plates at a predetermined temperature after cookingcompletes.

The control system may use a closed loop transfer function to regulatecooking temperature to ensure that the food item is cooked according tothe selected cooking preference.

The control system may calculate the total amount of energy required tocook the food item according to the cooking profile based on the weightof the food item and a temperature difference between cookingtemperature and initial food item temperature.

The control system may calculate the total amount of energy required tocook the food item according to the cooking profile using the followingequation, wherein Q is the total amount of energy required to cook thefood item according to the cooking profile, C_(p) is the specific heatcapacity of the food item, M is the weight of the food item, T₂ is therequired (target) temperature to achieve the cooking preference and T₁is the initial food item temperature:

Q=Mc _(p)(T ₂ −T ₁)

The control system may calculate the amount of energy transferred to thefood item per unit time (e.g. per second) based on the thickness andweight of the food item.

Suitably, the control system calculates the amount of energy transferredto the food item per unit time (q) using the following equation, whereinΔT₁ is the temperature difference between a first plate (T_(plate 1))and the food item temperature (T_(food item temp)) per unit time and ΔT₂is the temperature difference between a second plate (T_(plate 2)) andthe food item temperature (T_(food item temp)) per unit time and R_(th)is the thermal resistance of the food item:

q=ΔT ₁R_(th) +ΔT ₂ R _(th), wherein ΔT=T _(plate 1/2) −T_(food item temp)

and, wherein the thermal resistance of the food item is calculated basedon the surface area of the food item in contact with the pair of plates,the thickness of the food item and the thermal conductivity of the fooditem.

The control system may automate the pair of plates to maintain contactwith the food item during cooking based on feedback from a platepressure sensor.

The control system may actuate a rack on the cooking apparatus to liftthe food item off a plate after completion of cooking.

In accordance with the invention, there is also provided a method ofcooking a food item using an apparatus comprising a pair of plates inbetween which a food item is to be cooked and at least one of the plateshaving a heating element for cooking a food item including the steps of:selecting a cooking preference; measuring a distance between the pair ofplates when the food item lies therebetween to determine thickness ofthe food item; measuring a weight of the food item; determining acooking profile for cooking the food item according to the cookingpreference based on at least one of the thickness of the food item andthe weight of the food item; calculating a total amount of energyrequired to cook the food item according to the cooking profile based onthe weight of the food item; calculating an amount of energy transferredper unit time to the food item based on the thickness of the food item;and controlling power supply to the heating element based on the amountof energy transferred per unit time to the food item to cook the fooditem.

The method may include determining a cooking temperature based on thecooking profile.

The method may include calculating the total amount of energy requiredto cook the food item according to the cooking profile based on theweight of the food item.

The method may include comparing the total amount of energy required tocook the food item according to the determined cooking profile and theamount energy transferred to the food item per unit time to determinethe percentage completion of cooking.

The method may include comparing the amount of energy transferred to thefood item to the total amount of energy required to cook the food itemat discrete intervals.

The method may include predicting when the food item is cooked bymonitoring the amount of energy transferred to the food item. The fooditem is predicted as cooked when the amount of energy transferred to thefood item substantially equals the total amount of energy required tocook the food item.

The method may include comparing the amount of energy transferred to thefood item to the total amount of energy required to cook the food itemduring the cooking process.

The method may include stopping the power supply to the heating elementonce the energy transferred to the food item is equals the amount ofenergy required to cook the food item.

The method may include reducing the power supply to the heating elementto maintain the plates at a predetermined temperature after cookingcompletes.

The method may include using a closed loop transfer function to regulatecooking temperature to ensure that the food item is cooked according tothe selected cooking preference.

The method may include calculating the total amount of energy requiredto cook the food item according to the cooking profile based on theweight of the food item and a temperature difference between cookingtemperature and initial food item temperature.

The method may include calculating the total amount of energy requiredto cook the food item according to the cooking profile using thefollowing equation, wherein Q is the total amount of energy required tocook the food item according to the cooking profile, C_(p) is thespecific heat capacity of the food item, M is the weight of the fooditem, T₂ is the required (target) temperature to achieve the cookingpreference and T₁ is the initial food item temperature:

Q=Mc _(p)(T ₂ −T ₁)

The method may include calculating the amount of energy transferred tothe food item per unit time (e.g. per second) based on the thickness andweight of the food item.

Suitably, calculating the amount of energy transferred to the food itemper unit time (q) uses the following equation, wherein ΔT₁ is thetemperature difference between a first plate (T_(plate 1)) and the fooditem temperature (T_(food item temp)) per unit time and ΔT₂ is thetemperature difference between a second plate (T_(plate 2)) and the fooditem temperature (T_(food item temp)) per unit time and R_(th) is thethermal resistance of the food item:

q=ΔT ₁R_(th) +ΔT ₂ R _(th), wherein ΔT=T _(plate 1/2) −T_(food item temp)

and, wherein the thermal resistance of the food item is calculated basedon the surface area of the food item in contact with the pair of plates,the thickness of the food item and the thermal conductivity of the fooditem.

The method may include automating the pair of plates to maintain contactwith the food item during cooking based on feedback from a platepressure sensor.

The method may include lifting the food item off a plate aftercompletion of cooking.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are hereinafter described by way ofexample only, with reference to the accompanying drawings, wherein:

FIG. 1 is a flow chart illustrating the sequence of messages displayedon the user interface during the cooking process according to one formof the invention.

FIG. 2 is a flow chart illustrating the steps taken by the controlsystem during the cooking process according to one form of theinvention.

FIG. 3 is a flow chart illustrating the steps taken by the controlsystem to detect errors in the system according to one form of theinvention.

FIG. 4 is a perspective view of one embodiment of a cooking apparatus inaccordance with the present invention and having an ultrasonic sensoraccording to one form of the invention.

FIG. 5 is an enlarged view of an ultrasonic sensor on the cookingapparatus in FIG. 4 according to one form of the invention.

FIG. 6 is an enlarged view of a pivot of a lever arrangement of acooking apparatus including an angle sensor according to one form of theinvention.

FIG. 7 is a perspective view of a cooking apparatus including a lightbeam sensor according to one form of the invention.

FIG. 8 is a perspective view of a cooking apparatus including a slidersensor according to one form of the invention.

FIG. 9 is a perspective view of a cooking apparatus including a four-barlinkage handle according to one form of the invention.

FIG. 10 is a perspective view of a cooking apparatus with a rack forlifting the food item from the bottom plate after cooking according toone form of the invention.

FIG. 11 is a perspective view of a cooking apparatus with zoned cookingareas according to one form of the invention.

FIG. 12 is a block diagram schematically illustrating components of thecooking apparatus according to one form of the invention.

FIG. 13 is a flow chart illustrating the function of the control systemof the cooking apparatus according to one form of the invention.

FIG. 14 is a flow chart according to one form of the invention.

FIG. 15 illustrates the temperature profile of the core meat temperatureagainst the theoretical thermodynamic curve of Example 1.

FIG. 16 illustrates the temperature profile of the surface meattemperature against the theoretical thermodynamic curve of Example 2.

FIG. 17 illustrates the temperature profile of the core meat temperatureagainst the theoretical thermodynamic curve of Example 3.

DESCRIPTION

Several embodiments of the cooking apparatus in accordance with theinvention are illustrated. All embodiments generally relate to a cookingapparatus comprising a pair of plates in between which a food item iscooked. At least one of the plates has a heating element for cooking thefood item. The cooking apparatus further includes a user interface forselecting a cooking preference.

In one embodiment, the selected cooking preference determines theavailable cooking temperature profiles (hereinafter referred to as“cooking profile”) to cook the food item according to the userpreference.

A measurement sensor and a weight sensor on the cooking apparatusmeasures a distance between the pair of plates when a food item isplaced between the plates and the weight of the food item, respectively,and each of these sensors sends a signal to a control system (alsoreferred to as a controller) in the apparatus. The control systemcalculates the total amount of energy required to cook the food itemaccording to the cooking preference and the amount of energy to betransferred to the food item per unit time using either one or both ofthese signals.

A cooking profile is also determined by the control system, or may bepre-selected by a user, which specifies the cooking temperature or rangeof cooking temperatures for cooking the food item according to thecooking preference using the calculated total amount of energy. Thecontrol system then controls the heating element to cook the food itemto a desired result.

A flowchart illustrating the sequence of messages displayed on the userinterface during the cooking process according to one embodiment of theinvention is shown in FIG. 1. Once the user commences the cookingprocess by pressing the Start button on the user interface, the controlsystem heats the plates in a “Preheating” step to a cooking temperaturedetermined by the cooking profile. During the preheating step, thecontrol system determines the power required for the subsequent“Waiting” step while preheating step is being carried out.

Once the preheating step is completed, the control system applies thepower determined for the “Waiting” step to maintain the heated plates atthe cooking temperature. The power required for the subsequent “Cooking”step is determined during the “Waiting” step. Once a food item is placedon the plate, the “Cooking” step commences to cook the food itemaccording to the cooking profile by ensuring the plates are maintainedat the cooking temperature.

The control system also performs a series of checks to identify errorsin the system and minimize undesirable operating conditions (see FIG.3).

In order to cook a food item, the control system calculates the totalenergy (Q) required to cook the food item according to the cookingprofile and calculates the energy that has to be transferred per unittime (q) to the food item in order to cook the food item according tothe cooking profile. The amount of energy transferred per unit time tothe food item is measured against the total amount of energy required tocook the food item according to the cooking profile. The cooking processcompletes when the amount of energy transferred into the food itemequals the total amount of energy required to cook the food item.Namely, this occurs when:

Q=qt,

where t is the cooking time.

The amount of energy transferred per unit time to the food item may beregularly monitored and compared against Q. The cooking process stopswhen the calculated total amount of energy is transferred to the fooditem.

Alternatively, the time (t) taken to transfer the total amount of energy(Q) to cook the food item is calculated from the amount of energytransferred per unit time, and the cooking process stops when t isreached.

The control system calculates the total energy (Q) required to cook thefood item according to the cooking profile based on the measured weight(M) of the food item, the specific heat capacity (c_(p)) of the fooditem, the required temperature (T₂) to achieve the preferred cookingoutcome and the initial food item temperature (T₁) using the followingequation:

Q=Mc _(p)(T ₂ −T ₁)

he specific heat capacity of the food item is estimated from literature,for example, from The Engineering ToolBox (www.engineeringtoolbox.com).It may also be derived empirically or may be a combination of literatureand empirical values.

The required temperature may be obtained from literature, for example,Green, Aliza, Field Guide to Meat, 2005, and/or empirically, by visualinspection of the food item.

The control system calculates the energy transferred per second to thefood item (q) using the following equation where ΔT_(top) is thetemperature difference between the top plate and the food itemtemperature per unit time, ΔT_(btm) is the temperature differencebetween the bottom plate and the food item temperature per unit time andR_(th) is the thermal resistance of the food item:

q=ΔT ₁R_(th) +ΔT ₂ R _(th), wherein ΔT=T _(plate 1/2) −T_(food item temp)

The food item temperature is cumulative, adding the incrementaltemperature gain to the previous temperature value.

The thermal resistance of the food item is calculated using thefollowing equation:

$R_{th} = \frac{kA}{x}$

wherein A is the surface area of the food item in contact with theplates, x is the measured thickness and the k is the thermalconductivity of the food item.

The surface area (A) of the food item is calculated using the measuredthickness (x) and weight (M) of the food item, and the density (ρ) ofthe food item using the following equation:

$A = \frac{M}{x\rho}$

The density of the food item is estimated from literature. It may alsobe derived empirically or may be a combination of literature andempirical values.

One form of the cooking apparatus 10 is illustrated in FIGS. 4 and 5.

The cooking apparatus 10 comprises a horizontally arranged top plate 12Aand a bottom plate 12B in between which a food item is cooked, whereineach plate has a heating element (not shown) for cooking the food item.

In another embodiment, the pair of plates may be oriented at any anglefrom a horizontal to a vertical position.

The angle of the pair of plates may allow fluids such as oil orrendering to flow from a food item to reduce fluids from soaking thefood item. The angle of the pair of plates, for example, when positionedin a substantially vertical position may allow the food item to bereleased from the cooking apparatus when the cooking has completed ontoa tray or rack positioned below the cooking apparatus.

The top plate 12A is linked to the bottom plate 12B by a handle 18,whereby the handle 18 is levered to the cooking apparatus 10 to open andclose plate 12A and plate 12B (FIG. 6). Handle 18 is substantially ‘U’shaped in that it has a gripping bar 18A that extends across a front ofthe apparatus 10, which is where a user takes hold of the handle, andside arms 18B that extend from each side of the gripping bar down theside of the apparatus to each return at the rear of the apparatus andconnect to a rear hinge 13 fixed to the rear of the bottom plate 12B.Rear hinges 13 provide the pivot point that allows handle 18 to lever upand down in order to open and close the top plate 12A of the cookingapparatus. Each side of the top plate 12A is pivoted to the handle 18through a pivot pin 22 that is mounted on each of the handle's side armsat a point (approximately midway) between the gripping bar and the rearhinge. The top plate 12A is rotatable about pivot pins 22 so that thetop plate 12A ‘floats’ on pins 22 as the cooking apparatus is opened bylevering the handle 18 upward. This floating effect is useful toaccommodate uneven-shaped food items and to maximize contact of the topplate 12A on the food item.

The cooking apparatus 10 includes a weight sensor 13, and a measurementsensor 14 for measuring a distance between the pair of plates. Themeasurement sensor 14 may take many forms for measuring the distancebetween, i.e. the separation of, the plates. For example, themeasurement sensor may be a position, angle or displacement sensorusing, for instance, an electro-mechanical device (such as a straingauge) or a transformer or transducer (such as a piezo-electrictransducer). It is understood that the examples of sensors provided areillustrative only and that any suitable type of sensor may beincorporated into the cooking apparatus 10.

The cooking apparatus 10 also includes a user interface 820 in the formof a control panel 16 for transmitting data on cooking variables fromthe user (i.e. the cooking preference) to the control system 870. Theuser variables are used to determine the cooking profile.

The user interface includes a display device 830 which provides a visualindication of the user selection and a user input device 840 for theuser to enter data on the cooking variables.

The control system 870 receives signals from the measurement sensor 14,the weight sensor 13 and the control panel 16 to calculate the totalamount of energy required to cook the food item and to calculate theamount of energy being transferred to the food item during the cookingprocess, which in turn, is used to control the heating elements on thepair of plates, namely to ensure the temperature on the plates ismaintained at the cooking temperature.

The cooking apparatus described herein automates and controls cookingbased on the total amount of energy required to cook the food item andthe amount of energy per unit time transferred to the food item. Thisallows the food item to be cooked consistently to the preferred cookingoutcome regardless of the thickness or weight of the food item.

In contrast, a conventional comparable cooking apparatus would rely onmanual inspection and adjustment of a food item by a user to control thecooking process. This is time consuming and often inconvenient for auser who has to watch and move the food item on the cooking apparatus asneeded.

The cooking apparatus 10 takes into account the type of food itemcooked. Different types of food such as red meat, fish and chicken cookat different rates at the same temperature. As such, there is a lowlikelihood of overcooking or undercooking a food item with the describedcooking apparatus.

The cooking apparatus 10 allows a user to automate the cooking processwithout requiring the user to tend to the food item during the cookingprocess to produce consistently cooked food items. It achieves this byselecting a cooking preference (i.e. selecting the type of food item andpreferred cooking outcome) which determines the cooking profilesavailable to cook the food item to the desired cooking outcome.

Based on the weight and thickness of the food item, a cooking profile isdetermined which in turn determines the cooking temperature or range ofcooking temperatures to cook the food item. The control system 870calculates the total energy required to cook the food item to thepreferred cooking outcome and the amount of energy to be transferred tothe food item per unit time. The calculated amount of energy istransferred to the food item to cook the item to the desired cookingoutcome.

The weight sensor 13 is a load cell embedded within bottom plate 12B.The measurement sensor 14 measures the distance between the pair ofplates. The measurement sensor 14, in the embodiment of FIGS. 4 and 5,is an ultrasonic sensor mounted on the bottom plate 12B. The ultrasonicsensor may be mounted anywhere along the edge of bottom plate 12B and isassociated with a projection 20 on top plate 12A that reflects a signalfrom the ultrasonic sensor. The ultrasonic sensor operates similar toknown ultrasonic sensors in that the distance between the pair of platesis determined by the time taken for a signal to return to the sensor 14after reflecting off the projection 20 on the top plate 12A.

The projection 20 may be located on the handle 18 instead of top plate12A, as handle 18 is associated with movement of the top plate.Accordingly, the position of the projection 20 on the handle 18, whenthe top plate 12A contacts a food item placed on bottom plate 12B, isused by the ultrasonic sensor to calculate the distance between the pairof plates.

In another embodiment of the cooking apparatus (illustrated in FIG. 6),the measurement sensor 14 is an angle sensor located at the pivot pointat rear hinge 13 through which the top and bottom plates are pivoted. Asthe handle 18 is levered to receive a food item such as a steak betweenthe pair of plates, the sensor 14 measures the angle of the pivot at therear hinge compared to a reference point, such as fully closed positionwith no food item between the plates. From the angle of pivot thedistance between the pair of plates can be calculated by determining acorresponding change in angle through which the handle is pivoted.

In the embodiment illustrated in FIG. 7, the measurement sensor 14 is anoptical position sensor that includes a curtain of light beams mountedalong the edge of the bottom plate 12B. The curtain of light beams areassociated with a blocking cover 21 and the sensor measures the distancebetween the pair of plates based on the number of beams disrupted orblocked by a blocking cover 21.

The blocking cover 21 is mounted on the top plate 12A and is positionedto disrupt or block the curtain of discrete light beams as the distancebetween the pair of plates decreases. For example, in an inoperativeposition whereby the top plate 12A is at a maximum distance from thebottom plate 12B, the light beams are completely exposed. As the topplate 12A is lowered towards the bottom plate 12B, the blocking cover 21gradually covers a number of light beams, such that all the light beamsare completely blocked when the top plate 12A contacts the bottom plate12B. The sensor 14 measures the distance between the pair of platesbased on the number of light beams covered by the blocking cover 21(FIG. 7).

The blocking cover 21 may alternatively be located on a side arm of thehandle 18 rather than of the top plate 12A. In that embodiment, thenumber of light beams covered by the blocking cover 21 on handle 18 whenthe top plate 12A contacts a food item placed on bottom plate 12B isused controller to calculate the distance between the pair of plates.

In the embodiment of the cooking apparatus illustrated in FIG. 8, themeasurement sensor 14 comprises a sliding pin 14A that is mounted to aprinted circuit board located within the bottom plate 12B at one end andmovably connected to a guide 23 that is mounted to handle 18 at theother end. The guide 23 has a slot to receive sliding pin 14A such thatas the top plate 12A moves towards the bottom plate 12B, the sliding pin14A moves proportionally with the distance between the pair of platesalong a track 14B to transmit a signal to the control system to measurethe distance between the pair of plates (FIG. 8). The distance moved bythe sliding pin 14A along the track provides an indication of theseparation between the top and bottom plates.

The cooking apparatus may include more than one measurement sensor. Forexample, a pair of measurement sensors may be located on diametricallyopposed corners of one plate. This arrangement allows the control systemto determine an average separation between the pair of plates based onan average reading of the distances between each measurement sensor.This can be used to determine the thickness of unevenly-shaped fooditems.

FIG. 14 is a flow chart according to an embodiment of the invention.

In operation, a user uses the control panel 16 to select the cookingpreference by selecting settings such as the type of food item to becooked and preferred cooking outcome for the food item. For example, auser can cook a piece of steak to “medium” by pressing the appropriatebuttons on control panel 16 (Step (A) in FIG. 14). The user's selectionwill be transmitted to the control system.

The food item is placed onto the bottom plate 12B and the handle 18 ismoved to contact the top plate 12A with the steak.

The top plate 12A is connected to the handle 18 about the pivot pin 22to form a self-centering top plate whereby the top plate 12A self-pivotson the contour of the food item (FIG. 4). In this embodiment, the pairof plates may not be parallel to each other during the cooking process.This embodiment is suitable for uneven shaped food items such as a wholechicken or fish, whereby the pivotable nature of the top plate 12Aallows maximum contact of the top plate 12A with the food item.

In another embodiment of the cooking apparatus, the top plate 12A isconnected to the handle 18 by a four-bar linkage (FIG. 9). As inprevious embodiments, the handle side arms are linked to the bottomplate 12B through rear hinge 13, but the top plate 12A is further linkedto the bottom plate 12B by a pair of short arms 19 which connect thepair of plates in a diagonal fashion and which short arms 19 areparallel to the handle side arms. As illustrated in FIG. 9, short arm 19is connected toward the rear of the bottom plate 12B at one end andconnected to the front of the top plate 12A at the other end to form alink between the pair of plates.

This arrangement maintains the top plate 12A parallel to the bottomplate 12B regardless of the contours of the food item. This embodimentis suitable for flat-shaped food items such as a piece of steak or afish fillet which do not require the top plate 12A to pivot to maintainmaximum contact with the food item.

Once the top plate 12A contacts the food item by levering the handle 18about the rear hinge 13, the control system uses the weight signal fromthe weight sensor 13 and/or the measurement signal from the measurementsensor 14 to calculate the total amount of energy required to cook thefood item and to determine a cooking profile (Step (B) of FIG.14).Alternatively, the cooking profile may be selected by a user.

The determined cooking profile specifies how the food item is to becooked using the calculated total amount of energy by determining thetemperature or a range of temperatures at which the food item is to becooked (Tc in Step (C) of FIG. 14). For example, the food item may besubjected to (i) a high searing temperature for a short period of time(Cooking profile (1) in Step (B) of FIG. 14), (ii) a lower searingtemperature for a longer period of time followed by a constant lowtemperature “warming” heat (Cooking profile (2) in Step (B) of FIG. 14)or (iii) a low cooking temperature for an extended period of time(Cooking profile (3) in Step (B) of FIG. 14). Each of these cookingprofiles transfers the same amount of energy to the food item at the endof the cooking process. In an alternative embodiment, Steps (B) and (C)can occur at the same time.

The plates 12A and 12B are then preheated to the determined temperature.The cooking process completes when the amount of energy transferred intothe food item equals the total amount of energy required to cook thefood item.

Throughout the cooking process the control system 870 regularly comparesthe amount energy transferred to the food item per unit time against thetotal amount of energy required to cook the food item (according to thedetermined cooking profile) to determine when the cooking process iscompleted, and to additionally determine the percentage of completion ofthe cooking process, which is displayed on the display device 830.

The control system performs various functions including:

(a) determining a cooking profile for cooking the food item according tothe cooking preference based on the user's selection and at least one ofthe thickness and weight of the food item; (b) switching on the heatingelement;

(c) determining a time that has lapsed since the heating element isswitched on;

(d) determining a cooking temperature of the heating element based onthe cooking profile from the time since the heating element is switchedon;

(e) measuring a temperature of the heating element; and

(f) controlling the heating element to either increase or decrease aninput current based on the cooking temperature and the currenttemperature of the heating element to thereby either increase ordecrease the temperature of the heating element;

(g) calculating the total amount of energy required to cook the fooditem according to the cooking profile based on the weight of the fooditem;

(h) calculating the amount of energy transferred to the food item persecond based on the weight of the food item and the distance between thepair of plates (i.e. the thickness of the food item); and

(i) controlling the heating element to stop transfer of energy into thefood item once the energy transferred to the food item equals the totalenergy required to cook the food item.

FIG. 13 demonstrates some of the above functions of the control systemand the functional relationships between the control system and the userinterface, sensors and plates.

FIG. 12 illustrates the physical relationship of the components of thecooking apparatus.

The temperature sensor 810 provides real time information on the platetemperature to indicate to a user when to load the food item into theapparatus.

As discussed above, a temperature sensor 810 could be embedded into oneor both of top plate 12A and bottom plate 12B to determine the startingtemperature of the food item. A signal transmitted from the temperaturesensor 810 to the control system could be used to adjust the cookingtemperature and/or cooking time if, for example, a food item is placedin between the plates before a pre-heat temperature is reached.

The present cooking apparatus has the ability to control the cookingprocess by taking into account the thickness and weight of the fooditem. This means that the cooking apparatus can apply a shorter cookingtime to the food item to achieve a desired cooking outcome, without therisk of overcooking or undercooking the food item.

The cooking apparatus may include other optional features to enhanceusability or improve cooking outcomes. For example, the control panel 16may include a memory for saving parameters such as specific heatcapacity values and thermal conductivity values. These parameters can beentered by a user.

As illustrated in FIG. 10, the cooking apparatus 10 may also include arack 24 which is actuated to lift the food item away from the pair ofplates after completion of the cooking process. The rack 24 is mountedto the bottom plate 12B by an upwardly biased spring-loaded hinge 26.During the cooking process, the food item is placed on the rack and thetop plate 12A is lowered to contact the food item using the handle 18.As the top plate contacts the food item, the rack 24 is pushed onto andcontacts the bottom plate 12B. Accordingly, during the cooking process,the food item is in direct contact with the rack 24 which is in turnheated by the bottom plate 12B.

Once cooking is finished, the handle is either manually or automaticallymoved to lift the top plate away from the food item. Without thepressure of the top plate against the food item, the spring-loaded hinge26 lifts rack 24 off the bottom plate 12B to allow the food item to restin a warm position but away from direct heat.

In another embodiment of the cooking apparatus, the bottom plate 12Bincludes an embedded plate pressure sensor 800 to transmit a signal tothe control system in response to any changes in pressure on the plate.

The pair of plates may be controlled to move in response to a change inthickness or height of the food item. For example, loss of moisture froma piece of steak during cooking will result in shrinkage andconsequently, thickness of the piece of steak. As a result, the steakcould lose contact with the top plate 12A, which will affect the cookingprocess.

Furthermore, the pair of plates may be automated by the control systembased on the signal from the plate pressure sensor 800 to allow the pairof plates to move in response to any changes in thickness of the fooditem to maintain contact between the plates and the food item withoutexerting excessive pressure.

For example, a response from the control system to a change in pressureresulting from shrinkage of the steak would be to lower the top plate12A and restore contact with the steak, but without applying too muchpressure.

Additionally, the plate pressure sensor 800 can also detect whetherexcessive pressure has been exerted on the steak. In response, thecontrol system would raise the top plate 12A from the steak.

Continuous monitoring and movement of the pair of plates with anychanges in thickness of the steak ensures contact between the steak andthe pair of plates is maintained during the cooking process and ensuresthat the piece of steak is consistently cooked. Accordingly, the cookingapparatus is able to adjust cooking parameters and cooking functions inreal time during the cooking process in response to feedback fromvarious distance, pressure and temperature sensors.

As discussed above, the control system may automate the top plate 12A toraise the top plate from the steak. Removing the plate 12A from contactwith the food item reduces the likelihood of the food item overcooking.For example, in FIGS. 4 to 9 and 11, the top plate 12A may lift off thefood item to allow the food item to rest on the bottom plate.

In combination with the rack 24 positioned on the bottom plate 12B asdescribed above, upon completion of the cooking time the top plate maybe moved away from the food item and at the same time, the rack raisesthe food item off the bottom plate. FIG. 10 illustrates this embodimentwhere the top plate 12A lifts off the food item which in turn causes therack 24 to be raised off the bottom plate 12B to allow the food item torest.

After the cooking process has concluded, the control system could beprogrammed to transmit an audio and/or visual signal to indicatecompletion of cooking to a user.

The cooking apparatus may furthermore include zoned cooking areas,whereby one heating element is positioned adjacent another heatingelement, whereby the heating elements are located on side by side twinpairs of plates to provide localized heating to one area of the cookingapparatus. FIG. 11 illustrates this embodiment.

Specifically, FIG. 11 shows heating elements positioned to create zones26A and 26B on the bottom plate 12B which are heatable to differenttemperatures. Corresponding heating elements are provided in twoindependently movable top plates 12A each overlying a zone 26A or 26B.Zones 26A and 26B comprise separate heating elements that are localizedto function independently to heat the corresponding zone based ondifferent cooking profiles that are controlled by separate controlpanels 16. This allows multiple food items to be cooked simultaneouslybased on different predetermined settings and/or cooking outcomes thatcan be programmed via separate control panels 16.

The cooking apparatus may include a cover such as a shell that coversthe pair of plates 12A and 12B during the cooking process so that thesplattering of fluids such as oil during the cooking process is reduced.The cover also allows the food item to rest in an enclosed space tominimize heat loss.

In another embodiment, the cooked food item is maintained at the targettemperature after completion of the cooking process to avoid the needfor a resting step (see Example 3). Advantageously, this prevents thecooked food item from getting cold before it is consumed.

EXAMPLE 1

Type: Beef steak

Weight: 198 g

Thickness: 13 mm

Target temperature (T₂): 63° C. (Medium)

Initial temperature (T₁): 17° C.

Cooking temperature: 190° C.

Thermal conductivity of beef: 0.780 W/mK

Cooking time: 55 seconds

The thermal conductivity of beef was determined empirically and takesinto consideration the thermal conductivity of beef and the plate.

The plates were pre-heated to 190° C. based on the user selection of“beef steak” and “medium”, rising at a rate of around 25° C. per minute.The core temperature of the steak was measured by inserted a temperatureprobe into the center of the steak.

The steak was cooked on the plates maintained at 190° C. for 55 seconds(from about 4:20 to about 5:15 in FIG. 15) and rested for 80 seconds toachieve the desired cooking outcome (from about 5:15 to 6:35 in FIG.15). The cooking time was based on the time taken to transfer thecalculated total amount of energy required to cook the food item to thefood item.

The temperature profile of the core meat temperature against thetheoretical thermodynamic curve is illustrated in FIG. 15, whichindicates that the actual core temperature of the steak follows thetarget temperature of 63° C. based on the required energy calculations.A visual inspection of the cooked steak also confirms that the steak wascooked to medium.

EXAMPLE 2

Type: Beef steak

Weight: 183 g

Thickness: 15 mm

Target temperature (T₂): 62° C. (Medium)

Initial temperature (T₁): 13° C.

Cooking temperature: 190° C.

Thermal conductivity of beef: 0.780 W/mK

Cooking time: 65 seconds.

The experimental set up is similar to Example 1. The temperature profileof the surface meat temperature against the theoretical thermodynamiccurve is illustrated in FIG. 16, which indicates that the actual surfacetemperature of the steak follows the theoretical thermodynamic curve.

The steak was cooked on the plates maintained at 190° C. for 65 seconds(from about 3:37 to about 4:42 in FIG. 15) and rested for 69 seconds toachieve the desired cooking outcome (from about 4:42 to 5:51 in FIG.15).

EXAMPLE 3

Type: Beef steak

Weight: 194 g

Thickness: 20 mm

Target temperature (T₂): 90° C. (Well done)

Initial temperature (T₁): 5° C.

Cooking temperature: 200° C.

Thermal conductivity of beef: 0.780 W/mK

Cooking time: 90 seconds.

The thermal conductivity of beef was determined empirically and takesinto consideration the thermal conductivity of beef and the plate.

The plates were pre-heated to 200° C. based on the user selection of“beef steak” and “well done”. The core temperature of the steak wasmeasured by inserted a temperature probe into the center of the steak.

The steak was cooked on the plates maintained at 200° C. for 90 seconds(from about 0:00 to about 01:30 in FIG. 17). Thereafter, the platetemperature is reduced to allow the steak to maintain the targettemperature of 90° C. without being removed from the plate to rest (fromabout 20:00 to 40:00).

The temperature profile of the core meat temperature against thetheoretical thermodynamic curve is illustrated in FIG. 17, whichindicates that the actual core temperature of the steak is maintained atthe target temperature of 90° C.

It will be understood to persons skilled in the art of the inventionthat many modifications may be made without departing from the spiritand scope of the invention.

1. A method of cooking a food item using an apparatus comprising a pairof plates in between which a food item is to be cooked and at least oneof the plates having a heating element for cooking a food item includingthe steps of: selecting a cooking preference; measuring a distancebetween the pair of plates when the food item lies there between todetermine a thickness of the food item; measuring a weight of the fooditem; determining a cooking profile for cooking the food item accordingto the cooking preference based on at least one of the thickness of thefood item and the weight of the food item; calculating a total amount ofenergy required to cook the food item according to the cooking profilebased on the weight of the food item; calculating an amount of energytransferred per unit time to the food item based on the thickness of thefood item; and controlling power supply to the heating element based onthe amount of energy transferred per unit time to the food item to cookthe food item.
 2. The method for cooking a food item according to claim1 including comparing the amount of energy transferred to the food itemto the total amount of energy required to cook the food item during thecooking process.